The present invention relates to laser instruments and in particular to laser instruments of the kind used to read or to detect light reflected from a target which is spaced from the laser instrument.
The present invention has particular application to a handheld scanner used for reading bar code labels.
The present invention embodies a retro-directive lens system in which a transmitted light beam is directed out along one path and the reflected light is collected along the same path.
Retro-directive lens systems of this kind present a problem of conducting a beam from a laser into the lens system in such a way that the structure for receiving the beam from the laser and for routing that beam onto and along the optical axis of the lens system does not produce excessive shadowing or obstruction of the light collected and focused by the retro-directive lens system.
It is an important object of the present invention to construct a trifocal, composite, single piece lens for a laser instrument and to incorporate the lens in a laser instrument in a way which avoids the problems of retro-directive lens systems as used in the prior art.
Other important objects of the present invention are: to minimize the physical size of the structure required for receiving the beam from the laser at an angle off the optical axis and for routing the received beam onto the optical axis; to incorporate such beam receiving and routing structure integrally into a one piece, composite lens; and to associate the beam receiving and routing structure and the other elements of the lens with the laser in a way that minimizes shadowing and obstruction of the reflected light collected and imaged by the composite lens.
It is a related object of the present invention to accomplish the objects noted above with a lens system that provides a substantial depth of field in operation of a laser instrument so that light reflected from the target can be detected or read within an extended range of distances of the target from the laser instrument.